1. Technical Field
The invention disclosed broadly relates to data processing technology and more particularly relates to cryptographic applications in data processing.
2. Background Art
References--The following copending patent applications are related to this invention and are incorporated herein be reference:
B. Brachtl, et al., "Controlled Use of Cryptographic Keys via Generating Stations Established Control Values", Ser. No. 55,502, filed March 1987 and assigned to IBM Corporation, and incorporated herein by reference.
S. M. Matyas, et al., "Secure Management of Keys Using Control Vectors", filed August 1988, and assigned to IBM Corporation, and incorporated herein by reference.
S. M. Matyas, et al., "Data Cryptography Operations Using Control Vectors", filed August 1988 and assigned to IBM Corporation, and incorporated herein by reference.
Introduction--Every day electronic funds transfer (EFT) systems electronically transfer billions of dollars between institutions and individuals. Such transactions cannot be processed safely unless user identities can be validated securely and the correct, unaltered transmission of messages between network nodes can be assured.
A personal identification number (PIN) is a secret number assigned to, or selected by, the holder of a debit or credit card used in an electronic funds transfer (EFT) or point of sale (POS) system. The PIN serves to authenticate the cardholder to the system. Cryptography is employed in EFT and POS systems to insure the confidentiality and integrity of PINs and other EFT transactions.
Cryptography is the transformation of intelligible information into apparently unintelligible form in order to conceal the information from unauthorized parties. Cryptography is the only known practical method to protect information transmitted through communications networks that use land lines, communications satellites and microwave facilities. It can also be used not only to protect the privacy of data, but also the integrity of data.
The cryptographic transformation of data is ordinarily defined by a selected algorithm, or procedure, under the control of a key. Since the algorithm is normally public knowledge, protection of the transformed, or enciphered, data depends on secrecy of the key. Thus, the key must be kept secret to prevent an opponent from simply using the known algorithm and key to recover the enciphered data. The protection of the data therefore hinges on protection of secret keys.
A new approach to Key Management is described in the above-mentioned copending application by S. M. Matyas, et al, which also provides a good background for this invention. The invention disclosed herein deals with cryptography PIN processing which has as its objective the application of cryptographic keys and methods to protecting the confidentiality and integrity of PINs during generation, translation, distribution, and verification whereas the S. M. Matyas, et al. copending patent application deals with the generation, distribution and management of the keys themselves.
In order for the PIN to function properly, it must be known only to the cardholder and to the financial institution or institutions capable of authenticating the cardholder, but to no one else.
The PIN must contain enough digits so that an adversary (cardfinder, thief or counterfeiter) would have little chance of finding a correct PIN via repeated guesses (or trial and error). But the PIN should not contain too many digits, otherwise it will slow down the transaction time. The longer the PIN the more difficult it is to remember and the greater the probability of an entry error. Four to six decimal digit PINs are the industry standard, although longer PINs are sometimes employed as a customer-selected option.
It is customary to place a limit on the number of consecutive incorrect PIN entries that a cardholder is allowed. Ordinarily, transactions are aborted after three incorrect PIN entries. This makes it difficult for an adversary to guess a correct PIN via PIN exhaustion. Card retention is also sometimes employed as a means to discourage unauthorized card usage.